Italic letters in generated axis tick labels

Question

I have an issue creating axis tick labels that combine italic letters and input of variables. Simply said, I want to call variables and insert text such as n = 1 below each label.

Here's an example with everything but the italic n:

require(ggplot2)

mpg$class <- as.factor(mpg$class)
counts <- rep(1:7, 1)

ggplot(mpg, aes(class, hwy)) +
  geom_boxplot() +
  scale_x_discrete(labels = paste(levels(mpg$class), "\nn = ", counts, sep = ""))

My first thought was to use the Unicode for an italic N, like I've done for superscript numbers in the past. But for some reason, the letter is too small & stylistically mismatched with the rest of the text. More importantly, in my real use-case, all Unicode characters for italic n appear to render out of alignment, depressed somewhere halfway between normal and subscript.

ggplot(mpg, aes(class, hwy)) +
  geom_boxplot() +
  scale_x_discrete(labels = paste(levels(mpg$class), "\n\U1D45B = ", counts, sep = ""))

So, I found the plotmath function ~italic(x) could be used to italicize letters. However, there's a clear and unexpected failure when I incorporate it in the paste() line for the x-axis tick labels. Note that the function does work in xlab()

ggplot(mpg, aes(class, hwy)) +
  geom_boxplot() + xlab(~italic("n")) +
  scale_x_discrete(labels = paste(levels(mpg$class), "\n", ~italic("n"), " = ", counts, sep = ""))

I have searched StackOverflow for similar cases. However, none of them need to call for variables:

Add greek letters to axis tick labels in R

Changing one character in axis tick labels to italic while keeping multiple lines

How to change into italic style one letter in R plot without adding a space

How to italicize part (one or two words) of an axis title

I have tried understanding how to use expression() and bquote() while being able to call variables, but I have been unable to produce anything functional.

At this point, any help is very appreciated!

Eldredge

wb parse(text=sprintf('atop("%s", italic(n)==%s)', levels(mpg$class), counts)) – Aletheaalethia

Answer 1

These days, you can use the ggtext package to style your text with some markdown/html decorations.

library(ggplot2)
library(ggtext)
#> Warning: package 'ggtext' was built under R version 4.1.1

mpg$class <- as.factor(mpg$class)
counts <- rep(1:7, 1)

ggplot(mpg, aes(class, hwy)) +
  geom_boxplot() +
  scale_x_discrete(
    labels = paste0(levels(mpg$class), "<br><i>n = ", counts, "</i>")
  ) +
  theme(axis.text.x = element_markdown())

^{Created on 2021-10-16 by the reprex package (v2.0.0)}

Steffie

Perfect! I previously failed using ggtext, but updating its dependencies and following this example solved my problem. – Stride

Answer 2

editing the answer of teunbrand above, to only italicize the n without italicizing the count itself: is by adding </i> in the end of the "<br><i>n = " to become "<br><i>n </i>= "

label will be: paste0(levels(mpg$class), "<br><i>n</i> = ", counts)

instead of: paste0(levels(mpg$class), "<br><i>n = ", counts, "</i>")

library(ggplot2)
library(ggtext)

mpg$class <- as.factor(mpg$class)
counts <- rep(1:7, 1)

# italicized count
ggplot(mpg, aes(class, hwy)) +
  geom_boxplot() +
  scale_x_discrete(
    labels = paste0(levels(mpg$class), "<br><i>n = ", counts,"</i>")
  ) +
  theme(axis.text.x = ggtext::element_markdown())


# not italicized count
ggplot(mpg, aes(class, hwy)) +
  geom_boxplot() +
  scale_x_discrete(
    labels = paste0(levels(mpg$class), "<br><i>n</i> = ", counts) 
  ) +
  theme(axis.text.x = element_markdown())

Italicized count

Not italicized count

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